PFOV (Permissive Field of View) clean-room reimplemented based on the algorithm described in http://roguebasin.roguelikedevelopment.org/index.php?title=Precise_Permissive_Field_of_View, though the general structure is more influenced by recursive shadow casting, as implemented in Shadow.hs. In the result, this algorithm is much faster than the original algorithm on dense maps, since it does not scan areas blocked by shadows.
Calculates the list of tiles, in
Bump coordinates, visible from (0, 0).
Compare steepness of
(p1, f) and
Debug: Verify that the results of 2 independent checks are equal.
The Y coordinate, represented as a fraction, of the intersection of
a given line and the line of diagonals of squares at distance
d from (0, 0).
Debug functions for PFOV:
Debug: calculate steeper for PFOV in another way and compare results.